This invention relates generally to service lifts, and more particularly, to service lifts of a particular configuration. By a service lift is meant a lift for vehicles such as garden tractors, golf carts, or the like, or optionally, larger vehicles such as automobiles or light trucks.
These vehicles are lifted to a level wherein the serviceman can gain convenient access to the underside of the vehicle for purpose of service, maintenance, or repair. While generally used with smaller vehicles such as garden tractors or golf carts, a suitably sized, heavy duty lift can also lift small or medium size automobiles for maintenance, service, or repair. Furthermore, it is also conceivable that such lifts may serve as a storage site for one vehicle, such as a car, atop the space normally occupied by another vehicle, assuming there is sufficient height in a garage or other storage facility to permit such lifting or "double decking".
Referring again to the use of the lift for servicing purposes, it is quite common, in the event of lifting a vehicle of rather large size, for the fork legs to deflect to a considerable extent. In this case, while there is absolutely no danger of the forks failing, or the vehicle sliding laterally from the lift, (provided of course, that it is used within its load rating,) there is a noticeable and sometimes severe reluctance on the part of mechanics to position themselves beneath a vehicle which appears to be straining the lift to or beyond its capacity.
Thus, although a lift of the type described may have a nominal maximum load rating of 4,000 lbs., for example, mechanics will often not feel comfortable, or in fact will refuse to, work under a load of, for example, 2,500 lbs. on a 4,000 lbs. rated lift. This uncomfortable feeling develops from seeing the deflection of the forks, which is clearly visible. Thus, although the forks may take 15,000 or even 16,000 lbs. without failing, the apprehension of the mechanics takes place well within the rated load of the lift.
Accordingly, it has been discovered that the apprehension of these mechanics can be allayed by arranging a lift such that, in effect, it "leans back" or away from the direction of the load when the load is raised from the ground. In other words, this "leaning back" causes the outer ends of the fork legs to be gradually raised relative to the inner ends thereof as the lift frame passes through the curved section of the mast. Thus, under relatively heavy loads, the outer ends of the fork legs still appear to undergo little or no net deflection. This is because, as the load is tipped rearward, the apparent center of gravity of the load moves toward the rear and toward the supporting structure. This enables the supporting structure to share a greater portion of the load by reducing the effective overhanging or cantilevered force. Consequently, both the force and the leverage are decreased in respect to what they would otherwise be.
In this connection, for example, a preferred form of the invention calls for a pair of masts on the main frame to be bent or "pre-curved" through an angle totaling some 5.degree., preferably starting out with a negative angle of -1.degree. and working from there through the angle of 5.degree.. Thus, there is a net "lean back" angle of about 4.degree.. The curvature of the mast preferably is localized to a center section, such that two straight portions or elements are separated by a curved portion. Preferably, the masts are mounted such that 1.degree. is seen in the initial inclination of the mast towards the work or load, and the final angle of the second portion is 5.degree., leaving a net angle of 4.degree. back from a true vertical.
Of course, other amounts of curvature, as well as the location and length of the optionally but preferably included two straight legs of the curved or bent mast may vary somewhat within the scope of the invention. A deflection totaling some 5.degree. has proven most satisfactory for those applications in which it has been used. In another embodiment, a straight mast is used, with the mast being inclined at constant angle. This usually requires a mechanism to enable the forks to lie flat on the ground initially, and to assume a backward tilt as soon as they achieve substantial height.
In view of the failure of the prior art to provide a lift having at least one mast structure with a "backward lean" built into it, it is an object of the invention to provide a lift having at least one mast forming either all or a part of the main frame, with the mast having at least one curved portion leaning away from the direction of the load.
It is another object of the invention to provide a service lift with not only an improved capability for lifting loads, but also one which appears to the user to be much safer, particularly while lifting heavy loads.
Yet another object of the invention is to provide a service lift having a main frame with an optional longitudinal member and a pair of support legs extending transversely thereof, with such a main frame further including at least one mast preferably having a gradual curve therein, and most preferably having a curved section with straight elements lying to either side of the curved section.
Still another object of the invention is to provide a main frame with two channel-shaped masts each having curved sections flanked by two straight sections.
A further object of the invention is to provide a lift frame which cooperates with the curved masts including forks which move generally vertically under a force applied by a hydraulic or equivalent lifting mechanism.
A still further object of the invention is to provide a lift frame which includes a fork or a pair of forks with their legs extending initially outwardly and generally parallel to the support legs for the frame, and which forks legs are adapted to have their outer ends move up relative to their inner ends as the forks are raised.
An additional object of the invention is to provide a service lift with a lifting mechanism including components which are inherently capable of accommodating the slightly curved mast that the carriage of the lift frame follows as it moves up and down throughout its entire range of travel.
Another object of the invention is to provide an improved fork lift such as that described which optionally uses a hydraulic cylinder and flexible chains to apply its lifting force to the lift frame.
Yet another object of the invention is to provide a lift frame having a carriage with portions that move within two channels forming parts of the curved or inclined masts.
Still another object of the invention is to provide a service lift with a lift frame supported by a carriage having mast followers, such as rollers, skids, or the like, which are capable of remaining stabilized within the flanges of the mast as the lift frame moves through a path including curvilinear portions from the bottom to the top of the mast.
A further object of the invention is to provide a mast unit having appropriately shaped receptors for the rollers or the equivalent on the carriage of the lift frame, with such rollers or the like being arranged so as to closely track the profile of the mast unit.
A still further object of the invention is to provide a service lift which will not engender feelings of apprehension or refusal to work by mechanics called upon to position themselves under the forks of the lift, even when it is heavily loaded.
Another object of the invention is to provide a lifting unit wherein the masts are affixed to the walls of a building structure, to obviate the necessity of the remainder of the main frame.
A further object of the invention is to provide a lifting unit wherein the masts are straight but inclined rearwardly so that the carriage of the lift frame gradually undergoes a rearward movement as it rises, thereby inclining the lift fork or forks upwardly at their end portions and leaving them raised at all but the lowermost portion of their travel.
A still further object of the invention is to provide a straight-masted rear-tilted lift unit as described, wherein the carriage undergoes a pivoting or like movement near the bottom of its travel.
These and other objects of the present invention are achieved in practice by providing, in one embodiment, an improved lift assembly including a main frame having a longitudinally extending member, a pair of transverse support leg members, and a mast extending substantially vertically in use, a lift frame including a fork assembly, at least one carriage forming a part of the lift frame and a lifting mechanism for the lift frame, with the mast including a curved portion that extends in use generally away from the lateral direction in which the support legs extend. In another embodiment, a straight but inclined mast is employed, with the same net result of having the lift frame tilt backwards and positioning the load more over the main frame.
The manner in which these and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the a description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings in which like reference numbers indicate corresponding parts throughout.